amidiq - dae uptlax

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J. L. Arredondo-Figueroa et al./ Revista Mexicana de Ingeniería Química Vol. 6, No. 3 (2007) 301-308
Table 3. Average values (standard deviation) of physicochemical parameters
and nitrogenous compounds registered during the experiment.
Load rate (kg) Sample
points
pH T (°C) D.O
(mg/l)
TAN
(mg/l)
NH3
(mg/l)
194 FT 8.5
ST
BI
RT
a
(0.17)
8.5 a
(0.13)
8.4 a
(0.08)
8.5 a
20.5
(0.07)
a
(1.0)
20.5 a
(1.2)
20.4 a
(1.0)
19.6 a
6.4
(1.0)
a
(1.8)
4.6 b
(1.7)
5.8 a
(1.8)
7.2 a
1.96
(2.6)
a
(0.69)
1.03 b
(0.28)
0.36 c
(0.09)
0.26 c
0.11
(0.06)
a
(0.04)
0.07 a
(0.02)
0.01 b
(0.01)
0.02 b
(0.01)
156 FT 8.5
ST
BI
RT
a
(0.17)
8.4 a
(0.13)
8.3 a
(0.08)
8.5 a
19.1
(0.07)
a
(1.0)
19.0 a
(1.2)
19.0 a
(1.0)
19.0 a
7.7
(1.0)
a
(1.8)
5.9 b
(1.7)
6.1 a
(1.8)
7.0 a
1.73
(2.6)
a
(0.33)
0.91 b
(0.19)
0.37 c
(0.14)
0.22 c
0.08
(0.08)
a
(0.02)
0.06 a
(0.02)
0.01 b
(0.01)
0.01 b
(0.01)
89 FT 8.6
ST
BI
RT
a
(0.17)
8.5 a
(0.13)
8.3 a
(0.08)
8.6 a
18.9
(0.07)
a
(1.1)
19.6 a
(1.2)
18.9 a
(1.0)
18.0 a
7.0
(1.0)
a
(1.8)
5.4 b
(1.7)
6.3 a
(1.8)
7.4 a
1.27
(2.6)
a
(0.42)
0.64 b
(0.08)
0.25 c
(0.05)
0.22 c
0.07
(0.04)
a
(0.02)
0.05 a
(0.01)
0.01 b
(0.01)
0.01 b
(0.01)
a,b,c
Different superscript letters in columns, mean significant differences (p ≤ 0.05)
FT = Fish tank; ST = Settling tank; BI = Biofilter; RT = Reconditioning tank.
Preliminary tests results showed that all
requirement for a good nitrification rate in a wellaerated
culture system were fulfilled in this study;
presence of ammonia, dissolved oxygen, trace
nutrients, and a relative low level of organic carbon
in the biofilter. During the experimental period,
average water temperature varied between 18.0 and
20.5 °C. The highest values were registered during
the first phase of the experiment with no significant
differences (p ≥ 0.05) among sampling sites and
phases (Table 3). However, average temperature at
the reconditioning tank (RT) in the first phase was
slightly lower with respect to other sampling sites.
Dissolved oxygen fluctuated from 4.6 to 7.7
mg/l, the lowest values were observed in the settling
tank (ST), due that all wastes were accumulated and
concentrated in this site. Significant differences (p ≤
0.05) were observed among sampling sites
particularly in the ST, and it can be attributed to an
increase in water temperature. Oversaturated values
were registered in the fish tank (FT) and
reaconditioning tank (RT), where a vigorous aeration
was maintained throughout the experiment.
However, average oxygen concentration was 6.4
mg/l, a larger value than that required for complete
oxidation. Therefore, it can be assumed that it is
necessary to maintain an optimum growth and
survival rate of the rainbow trout (Klontz, 1991).
NO2 -
(mg/l)
0.44 a
(0.22)
0.64 b
(0.26)
0.41 a
(0.22)
0.24 c
(0.15)
0.41 a
(0.10)
0.61 b
(0.14)
0.40 a
(0.10)
0.25 c
(0.12)
0.44 a
(0.10)
0.59 b
(0.19)
0.32 c
(0.15)
0.28 c
(0.13)
NO3 -
(mg/l)
25.9 a
(4.5)
24.5 a
(2.6)
24.9 a
(3.4)
23.5 a
(3.1)
28.6 a
(3.4)
27.5 a
(2.8)
27.2 a
(2.2)
27.0 a
(3.6)
26.9 a
(4.6)
22.7 b
(9.0)
23.3 b
(8.3)
25.5 b
(3.5)
Results in Table 3 agreed with those reported
by Kruner and Rosenthal (1987) and Michaud et al.,
(2006) for fish culture systems. pH values were
almost constant throughout the experiment with
minor variations. These values had no significantly
differences (p ≥ 0.05) between sampling sites and
phases. Nitrification depends on the release of
inorganic nitrogen compounds from organic matter
usually degraded by heterotrophs. Normally,
nitrification rates are strongly influenced by pH. Srna
and Baggaley (1975) observed that the establishment
of nitrifying bacteria and conditions in which they
grow determine their response to pH changes.
Optimum pH for complete nitrification is circa 7.45,
effective nitrification is achieved within a pH range
of 7.0 to 8.2. Wild et al. (1971) reported that the
optimum pH for nitrification in freshwater was 8.4,
which coincides with the value found in our study.
Total ammonia nitrogen (TAN) range was
between 0.22 and 1.96 mg/l. The higher load fish
rate (194 kg) coincides with higher TAN value.
Significant differences (p ≤ 0.05) were observed
among load fish rates, with highly significant
differences in fish and settling tanks. Total ammonia
oxidation in the three load rates was similar
throughout the study meaning that metabolism of
nitrifying microorganisms were near their maximum
(Table 3). No adverse effects were observed on the